The use of 13C spin lattice relaxation times to study the interaction of alpha-methyl-D-glucopyranoside with concanavalin A

The spin lattice relaxation rates ($\text{1}\text{T}{}_1$) of the natural abundance ¹³C of all seven carbons of α-methyl-d-glucopyranoside were measured in the presence of Mn(II)-concanavalin A. The paramagnetic contribution to the relaxation rates was used to calculate the distance between the Mn(II) site and the saccharide. The results are consistent with the binding of the saccharide in a unique configuration on the surface of the protein with the ?CH₂OH (6 carbon) ~9Å, the ?CH₃ (7 carbon) 14Å, and carbons 1–5 about 10Å from the Mn(II). Notwithstanding the fact that these distances may be 10% or less in error, these data are in disagreement with a value of greater than 10Å between the saccharide and Mn(II) binding sites determined from X-ray diffraction studies by Edelman et al. ((1972) Proc. Nat. Acad. Sci. USA69, 2580–2584) and Hardman and Ainsworth ((1972) Biochemistry11, 4910–4919).